Systems and methods for synchronizing operations among a plurality of independently clocked digital data processing devices without a voltage controlled crystal oscillator

ABSTRACT

Example systems, apparatus, and methods receive audio information including a plurality of frames from a source device, wherein each frame of the plurality of frames includes one or more audio samples and a time stamp indicating when to play the one or more audio samples of the respective frame. In an example, the time stamp is updated for each of the plurality of frames using a time differential value determined between clock information received from the source device and clock information associated with the device. The updated time stamp is stored for each of the plurality of frames, and the audio information is output based on the plurality of frames and associated updated time stamps. A number of samples per frame to be output is adjusted based on a comparison between the updated time stamp for the frame and a predicted time value for play back of the frame.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority as a continuation of, U.S.patent application Ser. No. 13/724,048, filed on Dec. 21, 2012, for“Systems and Methods for Synchronizing Operations Among a Plurality ofIndependently Clocked Digital Data Processing Devices Without a VoltageControlled Crystal Oscillator,” which is a continuation of U.S. patentapplication Ser. No. 13/204,511, filed Aug. 5, 2011, for “Systems andMethods for Synchronizing Operations Among a Plurality of IndependentlyClocked Digital Data Processing Devices Without a Voltage ControlledCrystal Oscillator,” which is a continuation of U.S. patent applicationSer. No. 11/801,468, filed on May 9, 2007, for “Systems and Methods forSynchronizing Operations Among a Plurality of Independently ClockedDigital Data Processing Devices Without a Voltage Controlled CrystalOscillator,” which is incorporated herein by reference, which is acontinuation-in-part application which claims the benefit and priorityof U.S. patent application Ser. No. 10/816,217 filed on Apr. 1, 2004 for“System and Method For Synchronizing Operations Among a Plurality ofIndependently Clocked Digital Data Processing Devices,” which isincorporated herein by reference, which claims the benefit and priorityof U.S. Provisional Patent Application Ser. No. 60/490,768 filed on Jul.28, 2003 for “Method For Synchronizing Audio Playback Between MultipleNetworked Devices,” which is incorporated herein by reference; and thepresent application incorporates by reference U.S. Provisional PatentApplication Ser. No. 60/860,964 filed on Nov. 22, 2006 and U.S.Provisional Patent Application Ser. No. 60/876,455 filed on Dec. 20,2006, both for “Systems and Methods for Synchronizing Operations Among aPlurality of Independently Clocked Digital Data Processing Devices thatIndependently Source Digital Data.”

FIELD OF THE INVENTION

The present invention relates generally to digital content, and moreparticularly, to systems and methods for synchronizing operations amonga plurality of independently clocked digital data processing deviceswithout a voltage controlled crystal oscillator.

DESCRIPTION OF RELATED ART

Conventionally, playing the same digital content over multiple audioand/or audiovisual reproduction devices simultaneously or in synchronyis limited by the inherent differences in the frequencies or clock ratesof the crystal oscillators influencing the rates in which the digitalcontent is converted to analog content for playing over the respectiveaudio and/or audiovisual reproduction devices. Previous approaches thatsolve this problem require expensive hardware and/or circuitry, whichalso requires additional space within the audio and/or audiovisualreproduction device. There is thus a need for systems and methods forsynchronizing operations among a plurality of independently clockeddigital data processing devices without a voltage controlled crystaloscillator.

SUMMARY OF THE INVENTION

Exemplary systems and methods are provided that include a distributiondevice that maintains a clock rate and distributes a series of tasks toa group of execution devices (or synchrony group). Each task has aplurality of samples per frame associated with a time stamp indicatingwhen the task is to be executed. An execution device executes the seriesof tasks at the times indicated and adjusts the number of samples perframe in relation to the clock rate maintained by the distributiondevice. The synchrony group may also be configured to adjust samples perframe in relation to a clock rate maintained by the distribution device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an exemplary networked system;

FIG. 2 illustrates a functional block diagram of a synchrony grouputilizing a plurality of zone players formed within the exemplarynetworked system depicted in FIG. 1;

FIG. 3 illustrates a functional block diagram of a zone player for usein the networked system depicted in FIG. 1; and

FIG. 4 illustrates an exemplary digital framing methodology.

DETAILED DESCRIPTION

Referring to FIG. 1, an exemplary network audio system 10 is shown inwhich various embodiments of the invention may be practiced. Althoughthe term “audio” is used in connection with the exemplary network audiosystem 10, it will readily be appreciated that the herein describedsystems and methods may be employed with other forms of digital data,including visual and/or audiovisual digital data.

The exemplary network audio system 10 includes at least one zone player11, interconnected by a local network 12, all of which may operate underthe control of one or more user interface modules identified byreference numeral 13. The zone player 11 is sometimes referred to as adigital data processing device. One or more of the zone players 11 mayalso be connected to one or more audio information sources, which willgenerally be identified herein by reference numeral 14, and/or connectedto one or more audio reproduction devices, which will generally beidentified by reference numeral 15. It will be appreciated that thenumber of audio information sources may vary as among the various zoneplayers 11, and some zone players may not have any audio informationsources connected thereto.

A plurality of zone players 11 associated with a network audio system 10may be distributed throughout an establishment, such as residence, anoffice complex, a hotel, a conference hall, an amphitheater, auditorium,or other types of establishments as will be apparent to those skilled inthe art. For example, a zone player 11 and its associated audioinformation source(s) and audio reproduction device(s) may be located ina living room, another zone player may be located in a kitchen, anotherzone player may be located in a dining room, and other zone players maybe located in bedrooms, to selectively provide entertainment in thoserooms. The audio information sources 14 may be any of a number of typesof conventional sources of audio information, including, for example,compact disc (“CD”) players, AM and/or FM radio receivers, analog ordigital tape cassette players, analog record turntables and the like. Inaddition, the audio information sources 14 may comprise digital audiofiles stored locally on, for example, personal computers (PCs), personaldigital assistants (PDAs), or similar devices capable of storing digitalinformation in volatile or non-volatile form. The audio informationsources 14 may also comprise an interface to a wide area network such asthe Internet, or any other source of audio information, or an interfaceto radio services delivered over, for example, satellite. Audioinformation obtained over the wide area network may comprise, forexample, streaming digital audio information such as Internet radio,digital audio files stored on servers, and other types of audioinformation and sources as will be appreciated by those skilled in theart.

Generally, the audio information sources 14 provide audio informationassociated with audio programs to the zone players for playback. A zoneplayer that receives audio information from an audio information source14 that is connected thereto may provide playback and/or forward theaudio information, along with playback timing information, over thelocal network 12 to other zone players for playback. Users, using userinterface module 13, may also enable different groupings or sets of zoneplayers to provide audio playback of different audio programssynchronously.

Referring to FIG. 2, an exemplary group of execution devices (or“synchrony group”) 20 according to one embodiment of the invention isshown. The exemplary synchrony group 20 comprises synchrony group memberdevices or member devices including a master execution device 21 andzero or more slave devices 22(1) through 22(G) (generally identified byreference numeral 22(g)), all of which synchronously play an audioprogram provided by an audio information channel device 23. The audioinformation channel device 23 is sometimes referred to as a task sourceor a task distribution device. Each master execution device 21, slavedevice 22(g), and/or audio information channel device 23 may utilize azone player 11 as depicted in FIG. 1. The zone player 11 may function asan audio information channel device 23, a master execution device 21, ora slave device 22(g) for the synchrony group 20. The audio informationchannel device 23 may obtain audio information for the audio programfrom an audio information source 14, add playback timing information,and transmit the combined audio and playback timing information to themaster execution device 21 and slave devices 22(g) over local network 12(FIG. 1) for playback. The playback timing information that is providedwith the audio information, together with clock timing informationprovided by the audio information channel device 23 to the variousdevices 21 and 22(g), enables the master execution device 21 and slavedevices 22(g) of the synchrony group 20 to play the audio informationsimultaneously.

The master execution device 21 and the slave devices 22(g) receive theaudio and playback timing information, as well as the clock timinginformation, that are provided by the audio information channel device23, and play back the audio program defined by the audio information.The master execution device 21 also communicates with the user interfacemodule 13, controls the operations of the slave devices 22(g) in thesynchrony group 20, and controls the operations of the audio informationchannel device 23 that provides the audio and playback timinginformation for the synchrony group 20. Generally, the initial masterexecution device 21 for the synchrony group will be the first zoneplayer 11 that a user wishes to play an audio program. However, themaster execution device 21 may be migrated from a first zone player to asecond zone player, which preferably will be a zone player that iscurrently operating as a slave device 22(g) in the synchrony group.

In addition, under certain circumstances, the audio information channeldevice 23 may be migrated from one zone player to another zone player,which also may be a zone player that is currently operating as a memberof the synchrony group 20. It will be appreciated that the zone playerthat operates as the master execution device 21 may be migrated toanother zone player independently of the migration of the audioinformation channel device 23. For example, if a first zone player isoperating as both the master execution device 21 and the audioinformation channel device 23 for a synchrony group 20, the function ofthe master execution device 21 may be migrated to a second zone playerwhile the first zone player is still operating as the audio informationchannel device 23. Similarly, if a first zone player is operating asboth the master execution device 21 and the audio information channeldevice 23 for a synchrony group 20, the source function of the audioinformation channel device 23 may be migrated to a second zone playerwhile the first zone player is still operating as the master executiondevice 21. In addition, if a first zone player is operating as both themaster execution device 21 and the audio information channel device 23for a synchrony group 20, the master execution device 21 may be migratedto a second zone player and the audio information channel device may bemigrated to a third zone player.

The master execution device 21 receives control information from theuser interface module 13 for controlling the synchrony group 20 andprovides status information indicating the operational status of thesynchrony group 20 to the user interface module 13. Generally, thecontrol information from the user interface module 13 causes the masterexecution device 21 to enable the audio information channel device 23 toprovide audio and playback timing information to the synchrony group,allowing the devices 21 and 22(g) that are members of the synchronygroup 20 to play the audio program synchronously. In addition, thecontrol information from the user interface module 13 causes the masterexecution device 21 to enable other zone players to join the synchronygroup as slave devices 22(g) and/or to cause slave devices 22(g) todisengage from the synchrony group. Control information from the userinterface module 13 may also cause the zone player 11 that is currentlyoperating as the master execution device 21 to disengage from thesynchrony group, but prior to doing so, that zone player will cause thefunction of the master execution device 21 to transfer from that zoneplayer 11 to a second zone player, preferably to a second zone playerthat is currently a slave device 22(g) in the synchrony group 20. Thecontrol information from the user interface module 13 may also cause themaster execution device 21 to adjust its playback volume and/or toenable individual ones of the various slave devices 22(g) to adjusttheir playback volumes. In addition, the control information from theuser interface module 13 may cause the synchrony group 20 to terminateplaying of a current track of the audio program and skip to the nexttrack, and to re-order tracks in a play list of tracks defining theaudio program that are to be played by the synchrony group 20. Thestatus information that the master execution device 21 may provide tothe user interface module 13 may include such information as a name orother identifier for the track of an audio work that is currently beingplayed, the names or other identifiers for upcoming tracks, theidentifier of the zone player 11 that is currently operating as themaster execution device 21, and identifiers of the zone players that arecurrently operating as slave devices 22(g). In one embodiment, the userinterface module 13 may include a display that can display the statusinformation to the user. It will be appreciated that the zone player 11that is operating as the audio information channel device 23 for onesynchrony group may also comprise the master execution device 21 or anyof the slave devices 22(g) in another synchrony group. This may occurif, for example, the audio information source that is to provide theaudio information that is to be played by the one synchrony group isconnected to a zone player also being utilized as the master executiondevice or a slave device for the other synchrony group.

Referring to FIG. 3, a functional block diagram of an exemplary zoneplayer 11 constructed in accordance with one embodiment of the inventionis shown. The exemplary zone player 11 includes an audio informationsource interface 30, an audio information buffer 31, a playbackscheduler 32, a digital to analog converter 33, an audio amplifier 35,an audio reproduction device interface 36, a network communicationsmanager 40, a network interface 41, and a control module 42. In analternative system and method, the exemplary zone player 11 may notinclude the audio amplifier 35. In a further embodiment, the zone player11 includes and/or forms part of the audio reproduction device 15. Thezone player 11 also has a device clock 43 that provides timing signalsthat control the general operations of the zone player 11. In addition,the zone player 11 includes a user interface module interface 44 thatcan receive control signals from the user interface module 13 (FIGS. 1and 2) for controlling operations of the zone player 11, and providesstatus information to the user interface module 13.

Generally, the audio information buffer 31 buffers audio information, indigital form, along with playback timing information. If the zone player11 is operating as the audio information channel device 23 (FIG. 2) fora synchrony group 20, the information that is buffered in the audioinformation buffer 31 may include the audio and playback timinginformation that will be provided to the devices 21 and 22(g) in thesynchrony group 20. If the zone player 11 is operating as the masterexecution device 21 or a slave device 22(g) for a synchrony group (20),the information that is buffered in the audio information buffer 31 mayinclude the audio and playback timing information that the zone player11 is to play. The audio information buffer 31 may receive audio andplayback timing information from two sources, namely, the audioinformation source interface 30 and the network communications manager40. In particular, if the zone player 11 is operating as the audioinformation channel device 23 for a synchrony group 20, and if the audioinformation source is a source 14 connected to the zone player 11, theaudio information buffer 31 may receive and buffer audio and playbacktiming information from the audio information source interface 30.Alternatively, if the zone player 11 is operating as the audioinformation channel device 23 for a synchrony group 20, and if the audioinformation source is a source 14 connected to the network 12, or asource available over a wide area network, the audio information buffer31 may receive and buffer audio and playback timing information from thenetwork communications manager 40. However, if the zone player 11 isoperating as the master execution device 21 or a slave device 22(g) in asynchrony group 20, and if the zone player 11 is not also the audioinformation channel device 23 providing audio and playback timinginformation for the synchrony group 20, the audio information buffer 31may receive and buffer audio and playback timing information from thenetwork communications manager 40. It will be appreciated that, if thezone player 11 is not a member of the synchrony group, the zone player11 may not play this buffered audio and playback timing information.

According to some embodiments, the audio information source interface 30connects to the audio information source(s) 14 associated with the zoneplayer 11. While the zone player 11 is operating as the audioinformation channel device 23 for a synchrony group 20, and if the audioinformation is to be provided by a source 14 connected to the zoneplayer 11, the audio information source interface 30 will selectivelyreceive audio information from one of the audio information source(s) 14to which the zone player is connected and store the audio information inthe audio information buffer 21. If the audio information from theselected audio information source 14 is in analog form, the audioinformation source interface 30 will convert it to digital form. Theselection of the audio information source 14 from which the audioinformation source interface 30 receives audio information is under thecontrol of the control module 42, which, in turn, receives controlinformation from the user interface module through the user interfacemodule interface 44. The audio information source interface 30 addsplayback timing information to the digital audio information and buffersthe combined audio and playback timing information in the audioinformation buffer 21. More specifically, the audio information sourceinterface 30 receives audio information from an audio information source14, converts it to digital form if necessary, and buffers it along withplayback timing information in the audio information buffer 21. Inaddition, the audio information source interface 30 may also provideformatting and scheduling information for the digital audio information,whether as received from the selected audio information source 14 or asconverted from an analog audio information source. The formatting andscheduling information will control not only playback by the zone player11 itself, but will also enable other zone players that may be in asynchrony group for which the zone player 11 is the master executiondevice to play the audio program associated with the audio informationin synchrony with the zone player 11.

In one particular embodiment, the audio information source interface 30divides the audio information associated with an audio work into aseries of frames, with each frame comprising digital audio informationfor a predetermined period of time. As used herein, an audio track maycomprise any unit of audio information that is to be played withoutinterruption, or a series of one or more audio tracks that are to beplayed in succession. It will be appreciated that the tracks comprisingthe audio program may also be played without interruption, oralternatively playback between tracks may be interrupted by a selectedtime interval.

FIG. 4 depicts an illustrative framing strategy used in connection withone system and method of the invention for a digital audio streamcomprising an audio work. A framed digital audio stream 50 comprises asequence of frames 51(1) through 51(F) (generally identified byreference numeral 51(f)). Here, “(f)” may represent a generic sequencenumber for any particular frame (51), with the actual sequence numbersranging from “(1)” to “(F).” Each frame 51(f), in turn, comprises aseries of audio samples 52(f)(1) through 52(f)(S) (generally identifiedby reference numeral 52(f)(s)) of the audio track. The number of audiosamples 52(f)(s) may differ in each frame 51(f). Associated with eachframe 51(f) is a header 55(f) that includes a number of fields forstoring other information that is useful in controlling playback of theaudio samples in the respective frame 51(f). In particular, the header55(f) associated with a frame 51(f) includes a frame sequence numberfield 56, an encoding type field 57, a sampling rate information field58, a time stamp field 60, an end of track flag 61, and a length flagfield 62. The header 55(f) may also include fields for storing otherinformation that is useful in controlling playback.

Generally, the frame sequence number field 56 receives a number whichwill generically be the number “f,” from the range 1 through F as above,that identifies the relative position of the frame 51(f) in the sequenceof frames containing the digital audio stream 50. The encoding typefield 57 receives a value that identifies the type of encoding and/orcompression that has been used in generating the digital audio stream.Conventional encoding or compression schemes include, for example, MP3and WAV encoding and/or compression schemes, although it will beappreciated that other schemes may be provided for as well. The samplingrate information field 58 includes sampling rate information that mayindicate the sampling rate relative to the audio information channeldevice 23 and/or the sampling rate relative to a current inherent, clockrate of a synchrony group member. The condition of the end of work flag61 indicates whether the frame 51(f) contains the last digital audiosamples for the audio track associated with the framed digital audiowork 50. If the frame 51(f) does not contain the audio samples that areassociated with the end of the digital audio stream 50 for a respectiveaudio work, the end of work flag will be clear. On the other hand, ifthe frame 51(f) does contain the audio samples that are associated withthe end of the digital audio stream 50 for a respective audio work, theend of work flag 61 will be set. In addition, the length flag field 62will contain a value that identifies the number of audio samples in thelast frame 51(F) of the audio work 50. The time stamp field 60 stores atime stamp that identifies the time at which the zone player 11 is toplay the respective frame.

Within each synchrony group member, for each frame of a framed digitalaudio stream 50 that is buffered in the audio information buffer 21, theaudio information source interface 30, using timing information from thedigital to analog converter clock 34, may determine a time at which thezone player 11 is to play the respective frame, and will store a timestamp identifying the playback time in the time stamp field 60. The timestamp associated with each frame is used by the playback scheduler 32 todetermine when the portion of the digital audio stream stored in theframe is to be coupled to the digital to analog converter 33 to initiateplay back. It will be appreciated that the time stamps that areassociated with each of the frames in sequential frames will be suchthat they will be played back in order, and without an interruptionbetween the sequential frames comprising the digital audio stream 50. Itwill further be appreciated that, after a time stamp has been determinedfor the first frame and stored in frame 51(1) of a digital audio stream50, the audio information source interface 30 may determine time stampsfor the subsequent frames in relation to the number of samples in therespective frames and the current inherent clock rate of the synchronygroup member. The time stamps will also preferably be such that frameswill be played back after some slight time delay after they have beenbuffered in the audio information buffer 21.

In some embodiments, the zone players 11 are provided with a digital toanalog converter clock 34 whose time may be set by an element such asthe network communications manager 40. When a zone player 11 isoperating as a member of a synchrony group 20, its networkcommunications manager 40 may use the various types of timinginformation that it receives from the audio information channel device23 to adjust the time value of the synchrony group member's digital toanalog converter clock 34. If the clock's time value is to be adjusted,when the synchrony group member's network communications manager 40initially receives the current time information from the audioinformation channel device 23 for the synchrony group 20, the networkcommunications manager 40 may set the synchrony group member's digitalto analog converter clock 34 to the current time value as indicated bythe audio information channel device's current time information 23. Thenetwork communications manager 40 may set the digital to analogconverter clock 34 to the current time value indicated by the audioinformation channel device's current time information once, orperiodically as it receives the current time information.

After the network communications manager 40 receives a frame 51(f) fromthe network interface 41, it may also obtain, from the digital to analogconverter clock 34, the zone player 11's current time as indicated byits digital to analog converter clock 34. The network communicationsmanager 40 may determine a time differential value that is thedifference between the slave device's current clock time, as indicatedby its digital to analog converter clock 34, and the audio informationchannel device's time as indicated by the audio information channeldevice's clock timing information. Accordingly, if the slave device'scurrent time has a value TS and the audio information channel device'scurrent time, as indicated by the clock timing information, has a valueTC, the time differential value ΔT=TS−TC. If the current time of theslave device in the synchrony group 20, as indicated by its digital toanalog converter clock 34, is ahead of the audio information channeldevice's clock time, the time differential value will have a positivevalue. On the other hand, if the slave device's current time is behindthe audio information channel device's clock time, the time differentialvalue ΔT will have a negative value. If the zone player 11 obtains clocktiming information from the audio information channel device 23periodically while it is a member of the synchrony group 20, the networkcommunications manager 40 may generate an updated value for the timedifferential value ΔT when it receives the clock timing information fromthe audio information channel device 23, and may subsequently use theupdated time differential value.

The network communications manager 40 may use the time differentialvalue ΔT that it generates from the audio information channel devicetiming information and zone player 11's current time to update the timestamps that will be associated with the digital audio information framesthat the zone player 11 receives from the audio information channeldevice. For each digital audio information frame that is received fromthe audio information channel device, instead of storing the time stampthat is associated with the frame as received in the message in theaudio information buffer 21, the network communications manager 40 willstore the updated time stamp with the digital audio information frame.The updated time stamp is generated in a manner so that, when the zoneplayer 11, as a member of the synchrony group plays back the digitalaudio information frame, it will do so in synchrony with other devicesin the synchrony group.

The network communications manager 40 may utilize the updated timestamps associated with respective frames 51(f) to accommodate thecurrent inherent clock rate of the digital to analog converter clock 34of the synchrony group member. For example, when the synchrony groupmember's network communications manager 40 receives a first frame 51(1)having a time stamp having a time value T, it can generate an updatedtime value TU, and store the frame 51(1) with the updated time value TUin the audio information buffer 31 (e.g., 51(1)TU). In addition, sinceboth the number of samples in a frame and the current inherent clockrate of the digital to analog converter clock 34, which determines therate at which the samples in a frame are to be played by the synchronygroup member, are known to the network communications manager 40, thenetwork communications manager 40 can use that information, along withthe time value TU to generate an expected or predicted time value TE forthe time stamp of the next frame 51(2). After the synchrony groupmember's network communications manager 40 receives frame 51(2), it cangenerate the updated time value TU for frame 51(2) and compare that timevalue to the time value TE that was predicted for frame 51(2). If thetwo time values do not correspond, or if the difference between them isabove a selected threshold level, the clock that is used by the audioinformation channel device 23 to generate the time stamps is advancingat a different rate than the synchrony group member's digital to analogconverter clock 34, and the network communications manager 40 may adjustthe number of samples per frame to accommodate the current inherentclock rate of the digital to analog converter clock 34 of the synchronygroup member. If the two time values do correspond (e.g.,51(2)TE=51(2)TU), or the difference is below a threshold level, the timedifferential value is constant, and the network communications manager40 need not accommodate the current inherent clock rate of the digitalto analog converter clock 34 of the synchrony group member.

As an example of one way the network communications manager 40 adjuststhe number of samples in one or more frames to accommodate the currentinherent clock rate of the digital to analog converter clock 34 of asynchrony group member, consider a situation where the clock used by anaudio information channel device 23 indicates a sampling rate of 44105samples per second for the audio information channel device 23. Asynchrony group member with a digital to analog converter clock 34operating at a current inherent clock rate of 44100 samples per secondwill require the network communications manager 40 for the synchronygroup member to reduce the number of samples in one or more frames byfive samples for each one second interval that a particular track(s)comprising one or more frames are being played by the synchrony groupmember.

Continuing this example, a second synchrony group member with a digitalto analog converter clock 34 operating at a current inherent clock rateof 44110 samples per second will require the network communicationsmanager 40 for the second synchrony group member to increase the numberof samples in one or more frames by five samples for each one secondinterval that a particular track(s) comprising one or more frames isbeing played by the second synchrony group member. As a result of theindependent adjustments taking place within the first and secondsynchrony group members in relation to their shared audio informationchannel device 23, both synchrony group members will be playing the sameor nearly the same frame at the same time, despite the differences intheir respective current inherent clock rates.

An information channel device 23 may be configured to periodicallyreceive the respective current inherent clock rates of one or moresynchrony group members comprising a synchrony group. Using thisinformation, the audio information channel device 23 performs therequisite adjustments (instead of the respective one or more synchronygroup members) and sends one or more tracks to each synchrony groupmember, wherein the one or more tracks are adjusted to accommodate thecurrent inherent clock rates of the respective synchrony group members.Accordingly, as a result of the multiple adjustments taking place withinthe audio information channel device 23 with respect to the currentinherent clock rates of the one or more synchrony group members, allsynchrony group members may play the same or nearly the same frame atthe same time, despite the differences in their respective currentinherent clock rates.

The exemplary zone player 11 serving as a synchrony group member may ormay not include an audio amplifier 35 (FIG. 3). Further, as describedherein, an audio information channel device 23 may perform the requisitesample adjustments or each synchrony group member may perform therequisite sample adjustments. Provided the synchrony group member and/orthe audio reproduction device 15 (that is wired or wirelessly associatedwith the synchrony group member) includes at least one amplifier,regardless of scenario, the audio reproduction device 15 may adapt andmaintain as constant a current inherent clock rate of the synchronygroup member. Accordingly, the audio reproduction device 15 may play thesame or nearly the same frame at the same time as another synchronygroup member. This may be advantageous, because some audio reproductiondevices 15 may be incapable of making timely clock rate adjustments.Consequently, by adjusting samples per frame, some exemplary systems andmethods as described herein may function with audio reproduction devices15 that would otherwise be incompatible with those systems and methodsthat include clock rate adjustments for achieving a synchronousperformance.

While various systems and methods have been described above, it shouldbe understood that they have been presented by way of example only, andnot limitation. Thus, the breadth and scope of a preferred embodimentshould not be limited by any of the above-described exemplary systemsand methods.

The invention claimed is:
 1. A digital data processing devicecomprising: an interface to receive multimedia information arranged as aplurality of frames, each frame to include one or more samples and anindication of when to play the one or more samples in a frame; aninformation buffer to store the plurality of frames for play back by thedigital data processing device, wherein the digital data processingdevice is to receive clock information from a source device anddetermine a time differential value between the received clockinformation and clock information associated with the digital dataprocessing device, the time differential value to be applied with theindication of when to play each of the plurality of frames to store anupdated indication of when to play each of the plurality of frames inthe information buffer; and an output to play back one or more samplesin a frame from the information buffer according to the updatedindication of when to play the frame, wherein the digital dataprocessing device is to adjust, based on a comparison between theupdated indication of when to play the frame and a predicted time valuefor play back of the frame, a number of samples per frame that are to beplayed.
 2. The device of claim 1, further comprising a networkcommunications manager to receive the plurality of frames from an audioinformation source.
 3. The device of claim 1, wherein the adjustment ofthe number of samples per frame is also based on a clock rate of thedigital data processing device.
 4. The device of claim 1, wherein thedigital data processing device is among a group of digital dataprocessing devices and is to be designated as a master execution deviceconfigured to control the distribution of information among the group ofdevices.
 5. The device of claim 1, further comprising a user interfaceto control the digital data processing device.
 6. The device of claim 1,wherein the digital data processing device is configured to enableanother digital data processing device to join a group of digital dataprocessing devices.
 7. The device of claim 1, wherein the digital dataprocessing device is to transfer an ability to control the digital dataprocessing device such that another digital data processing devicebecomes a master execution device.
 8. The device of claim 1, wherein theindication of when to play the one or more samples in the framecomprises a time stamp.
 9. A method for synchronizing audio playback,the method comprising: receiving, by a playback device, audioinformation including a plurality of frames from a source device over anetwork, wherein each frame of the plurality of frames includes one ormore audio samples and an indication of when to play the one or moreaudio samples of the respective frame; updating the indication of whento play each of the plurality of frames using a time differential valuedetermined between clock information received from the source device andclock information associated with the playback device; storing theupdated indication of when to play each of the plurality of frames; andoutputting audio information based on the plurality of frames andassociated updated indications via the playback device; and adjusting,based on a comparison between the updated indication of when to play theframe and a predicted time value for play back of the frame, a number ofsamples per frame to be output.
 10. The method of claim 9, furthercomprising enabling the playback device to function as a masterexecution device configured to control distribution of information amongthe group of playback devices.
 11. The method of claim 10, furthercomprising enabling an additional playback device to join the group ofplayback devices.
 12. The method of claim 10, wherein audio informationis distributed to the group of playback devices using a selectedmulti-cast transmission methodology.
 13. The method of claim 10, furthercomprising migrating the distribution of audio information from oneplayback device to another playback device.
 14. The method of claim 10,further comprising distributing audio information to a second group ofplayback devices.
 15. The method of claim 9, further comprisinggenerating the predicted time value for the frame using the updatedindication of when to play a previous frame and a clock rate of theplayback device.
 16. The method of claim 9, wherein the comparisonfurther comprises comparing whether a difference between the updatedindication of when to play and the predicted time value exceeds athreshold level.
 17. The method of claim 9, wherein the indication ofwhen to play the one or more samples in the frame comprises a timestamp.
 18. A tangible computer-readable storage device includinginstructions executable by a processor, the instructions, when executedby the processor, configure the processor as a digital data processingdevice, the digital data processing device comprising: an interface toreceive multimedia information arranged as a plurality of frames, eachframe to include one or more samples and an indication of when to playthe one or more samples in a frame; an information buffer to store theplurality of frames for play back by the digital data processing device,wherein the digital data processing device is to receive clockinformation from a source device and determine a time differential valuebetween the received clock information and clock information associatedwith the digital data processing device, the time differential value tobe applied to the indication of when to play each of the plurality offrames to store an updated indication of when to play each of theplurality of frames in the information buffer; and an output to playback one or more samples in a frame from the information bufferaccording to the updated indication of when to play the frame, whereinthe digital data processing device is to adjust, based on a comparisonbetween the updated indication of when to play the frame and a predictedtime value for play back of the frame, a number of samples per framethat are to be played.
 19. The computer-readable storage device of claim18, wherein the adjustment of the number of samples per frame is alsobased on a clock rate of the digital data processing device.
 20. Thecomputer-readable storage device of claim 18, wherein the digital dataprocessing device is among a group of digital data processing devicesand is to be designated as a master execution device configured tocontrol the distribution of information among the group of devices. 21.The computer-readable storage device of claim 18, wherein the digitaldata processing device is configured to enable another digital dataprocessing device to join a group of digital data processing devices.22. The computer-readable storage device of claim 18, wherein thedigital data processing device is to transfer an ability to control thedigital data processing device such that another digital data processingdevice becomes a master execution device.
 23. The computer-readablestorage device of claim 18, wherein the indication of when to play theone or more samples in the frame comprises a time stamp.